Pressure control system



Nov. 22, 1932. su E 1,888,332

PRESSURE CONTROL SYSTEM Original Filed March 12, 1926 6'SheetsSheet 1Original Filed March 12, 1926 6 Sheets-Sheet 2 A INVENTOARZX'WMW BYM HlSATTORNEYS Nov. 22, 1932. SUMMEY 1,888,332

PRES SURE CONTROL SYSTEM Original Filed March 12, l926 6 Sheets-$heet 3INVENTO w? zbiifi HIS ATTORNEYS Nov. 22, 1932. D, S MMEY 1,888,332

PRESSURE CONTROL SYSTEM Original Filed March 12, 1926 6 Sheets-Sheet 4LQJ L J Fly 2 I 'm' HIS ATTORNEYS D. L. SUMMEY PRESSURE CONTROL SYSTEMNqv. 22, 1932.

Original Filed March 12, 1926 6 Sheets-Sheet 5 4. HIS ATTORNEYS INVENTORk9 My Patented Nov. 22, 1932 UNITED STATES PATENT orrlcr.

PRESSURE CONTROL SYSTEM Original application filed larch 12, 1926,Serial No. 94,334. Divided and this application filed September 21,1928. Serial No. 307,542.

This invention relates to pressure control systems.

This application is a division from an application filed March 12, 1926,Serial No. 94,334, patented March 8, 1932, Patent Number 1,849,044.

It is an object of the invention to provide a fluid pressure controlsystem in which the effective pressure may be automatically lim- 19 itedto one of a pluralit of critical pressures. With this general ob'ect,and others not specifically referred to, in view, the invention consistsin the features, combinations, details of construction and arrangementsof parts which will first be described in connection with theaccompaying drawings and then more particularly pointed out.

In the drawings, Figure 1 is a diagrammatic view of a fluid 2-3 pressuresystem having embodied therein a pressure control constructed inaccordance with the invention;

Figure 2 is a sectional view taken on the broken line 2-2 of Fig. 3, ofa hydraulic 5:5 valve unit;

Figure 3 is a sectional view taken on the broken line 33 of Fig. 2;

Figure 4 is a sectional view taken on the broken line 4-4 of Fig. 5;

Figure 5 is a sectional view (enlarged), taken on the line 55 of Fig.3;

F i Ire 6 is a similar view showing parts in a different position;

Figure 7 is a view partly in elevation and 3 partly sectional (enlarged)the section being taken on the line 77 of Fig. 2;

Figure 8 is a similar view showing parts in a different position;

Figure 9 is a View in vertical section, with parts in elevation, of partof a pressure limiting device, the section being taken on the line 9-9of Fig. 1 (and enlarged) Figure 10 is a. top plan view of another partof the pressure limiting device; Figure 11 is a sectional detail view;and

Figure 12 is a vertical sectional view (enlarged) taken on the line12-12 of Fig. 10.

Referring to the drawings, F ig.- 1 illustrates diagrammatically a fluidpressure control as applied to the pressure system of an extrusionpress. In this system certain press elements are actuated underrelatively high pressure and other elements under relatively lowpressure. As is more fully pointed out hereinafter, the invention in itsentirety ineludes means for automatically limiting the eifectivepressure to one of a plurality of predetermined critical pressures.

The press here shown as an example has a ram 115 mounted on a cross-head116 which so slides on suitable horizontal columns or tie rods (notshown). Crosshead 116 is moved to drive the ram forward b a hydraulicplunger 123 which is secur to the crosshead. This plunger operates in ahydraulic c5 cylinder 124 connected with the main ressure line, as laterdescribed. Cro'sshea 116 is withdrawn by means of two hydraulic plungers130, which operate in relatively small pull-back cylinders 132 which aredirectly connected with the main line. Being under constant, that is,continuous pump pressure, their tendency is to move the crosshead backbut because of their relatively small size they are effective only whenthe large cylinder 124 is under exhaust.

The billet to be extruded is held by a container 134 mounted on acrosshead 138 which slides on the tie rods above mentioned. Movement ofthe container crosshead 138 is effected by piston rods 142 to'which thecrosshead is connected and on which are pistons 143 operating inhydraulic cylinders 144. The crosshead 138. is moved in one direction,namely, towards the left, as viewed in Fig. 1, by variable, i. e.,valve-controlled pressure fluid, as later described, and in the oppositedirection by. constant return .pressure. As this constant returnpressure operates on a smaller piston area it becomes effective onlywhen the valve-controlled pressure is relieved.

Movable across the axis of the container bhamber and ram is areciprocating carrier slide 148 moved by a piston rod 149 to which it issecured and which has a piston operating in a hydraulic cylinder 1.50.This unit is operated in the same way as container crosshead, namely, byvariable pressure and constant return pressure.

This carrier slide, as explained in said parent application, carries thedie. To stop the carrier in die-centering position, a latch 164 isprovided which enters a notch 165 formed in the slide. The latch isattached to the end of a piston rod carried by the piston, 166 workingin an air cylinder 167, the air supply of which is controlled as laterreferred to. The air pressure normally holds the latch advanced in aposition to enter the notch. The latch is withdrawn by a coil spring 169bearing against the face of the piston and effective upon release of theair pressure.

The billet is inserted into the container by a billet pusher 170. Thispusher is carried on the end of a piston rod 174 having a piston workingin a hydraulic cylinder 17 5 operated by variable pressure and constantreturn pressure.

To sever the extruded stock from the stump a cutter is provided in theform oi drop bar shears 179. The cutter is connected to a piston 179working in a fluid pressure cylinder 180.

Figure 1 indicates a valve unit 323 for the hydraulic cylinder 124 ofthe main ram. Sinn ilar units are indicated at 327 for the containerpower unit, 329 for the slide power unit, 341 for the loading rain unitand 344 for the cutter unit. The drawings illustrate in detail anexample of these units.

Referring more particularly to Figs. 2-8, the valve unit there shownincludes a valve chest 428, having a valve chamber 427 with whichcommunicates an inlet pipe 429 for connection with a water pressureline, e. g. line 322. The valve chest has a second valve chamber 443communicating with an exhaust pipe 446 for connection with the wastewater line, e. g. line 320, which may lead back to the suction side ofthe pumps, e. g. pumps 321. The inlet valve chamber 427 is connectedwith a pressure outlet pipe 445, leading to the power cylinder, by meansof a transverse bore 440, a vertical bore 441, a second transverse bore442, the exhaust chamber 443 and passage 444. The exhaust valve chamberis in communication with power outlet pipe 445. through passage 444.Above the exhaust outlet in the exhaust chamber is a tubular valve seat447 on which seats an exhaust valve 448. The inlet valve is carried by avalve stem 430 which is connected by a coupling435 with a piston rod436, the piston 437 of which works in an operating air cylinder 438. Thepiston is operated by pressure fluid, e. g. compressed air, admitted toone end or the other of the cylinder. When the piston is raised it opensinlet valve 425 and when lowered it returns the valve to its seat. Theexhaust valve is carried by a valve stem 449 and is connected by acoupling, like coupling 435, with a piston rod 451. This latter is aduplicate of piston rod 436 and is actuated by a duplicating air unit.These duplicating parts are not shown in detail but the constructionwill be apparent from Figs. 2 and 3. In the present embodiment, the twoair cylinders are formed by a common cylinder block 452 with separatebottom closures 453, 454. The valve chest 428 and the common cylinderblock 452 are connected together by bolts 455, the united structurebeing mounted in any suitable manner.

When the exhaust valve 448 is closed and the inlet valve 425 opens thereis a flow of water from the main line through inlet pipe 429 to thepower outlet pipe 445 and thence to the cylinder of the hydraulic powerunit. When the inlet valve is closed and the exhaust valve open, thepressure water can exhaust back from the power unit through pipes 44-5and 446 to the exhaust line.

Figures 2 to 8 inclusive illustrate an automatic control for a valveunit. As shown, the front side of the cylinder block 452 has a flat face(Fig. The cylinder 438 for the inlet valve has an upper passage 460leading from the fiat face of the cylinder block to the interior of thecylinder above the piston, and a similar lower passage 461 leading to apoint below the piston. Bolted to the flat face of the cylinder block isa block 462 having a flat top face 463. Opening out of this flat face(Figs. 5, 6) are three vertical bores or passages 464, 465, 466, two ofwhich communicate with the air cylinder, the third being an exhaustpassage. To this end, as here shown, the block 462 has an uppertransverse passage or bore 467 leading from vertical bore 464 andregistering with cylinder passage 460 and a lower transverse passage 468leadin from vertical bore 465 and registering with cylinder passage 461.The block has a third transverse bore or passage 469, extending in'adirection opposite to bores 467, 468, and leading from the middlevertical passage 466 to an exhaust pipe or outlet 470. In the embodimentillustrated, a valve chamber 471 is formed by the fiat face 463 of theblock 462 and an open sided valve housing 472 bolted to the block 462.With this construction, the three vertical passages 464, 465, 466 opendirectly into the valve chamber. In the top of the valve housing 472 isan inlet pipe 473 for connection with a source of pressure fluid, e. g.compressed air. Operating in the valve chamber 471 and sliding on thetop face of block 462 above the three ports of the vertical passage, isa D-slide valve 474, its enclosed recess 475 being arranged to span theport of the middle passage (exhaust) and one or the other of the endports, depending on the valve position.

When the D-valve is in the position of Fig. 5, end passage 465 is opento the valve chamber,thus placing the lower end of inlet valve cylinder438 in communication with the pressure fluid. The D-valve spans themiddle pas sage 466 and end passage 464, thus placing the upper end ofcylinder 438 in communication with exhaust. The air passes from valvechamber 471 through passages 465, 468 and 461 to the cylinder and raisespiston 437, thereby opening the hydraulic inlet valve 425. Meanwhile airabove the piston exhausts via passages 460, 467, 464, valve recess 47 5,passages 466, 469 and pipe 470.

When the D-valve is moved, as later described, to the position of Fig.6, the flow is reversed. That is, passage 464 is open to the valvechamber and the air passes "via passages 467 and 460 to the upper partof cylinder piston 437, thus closing inlet valve 425.

, Meanwhile the air below the cylinder exhaust via passages 461, 468,465, valve recess 475, passages 466, 469 to pipe 470.

The D-valve 474 has two forked upright abutments 478, 479 between whichis freely mounted a rectangular block 480 on a piston rod 481, the rodbeing cradled in the forks of the abutments. This forms'a simpleconstruction by which the D-valve is moved upon movement of the pistonrod 481,

the block 480 moving against one abutment or the other. It also permitsthe D-valve to adjust itself to its seat. On one end of the piston rod481 is a relatively'large piston 482 having a packing ring 483 andsliding ina cylindrical extension 484 of the valve chamber. The end ofthis extension is closed by a plug cap 485. At the other end of thevalve chamber is'a cylindrical extension 486 substantially smallerthanextension 484 and open to atmosphere. In this extension 486 slides arelatively small piston 487 also mounted on the piston rod. This latterpiston serves as a bearing support for the piston rod and a closure forthe end of the valve chamber. The opposing inner faces of both pistonsare under valve chamber pressure but the inner area of piston 482 islarger than that of piston 487. Under normal conditions, therefore, andassuming the end of extension 484 to be open to exhaust, there is aconstant effective force, measured by the air pressure on the excess ofone piston area over the other, that moves the piston rod in onedirection, i. e. to the left as viewed in 5, 6. It may be moved in theopposite direction by admitting pressure to the outer end of extension484. With the unbalanced positi'on arrangement shown, air undersubstantially the same pressure as the valve chamber air may be used.When such pressure is admitted to extension 484, as presently described,the piston rod is moved in the opposite direction, i. e. to the right asviewed in Figs. 5, 6.

Opening out of the valve chamber 471 is a longitudinal passage 490formed in the body of the caslng 472 and communicating with a transversebore or passage 491 which leads to the outer face of the casing. Boltedto this face of the casing is a valve casin 492 having a valve chamber493 out of the lower end of which opens a transverse passage 494registering with passage 491. Opening out of the upper end of valvechamber 493 is a second transverse passage 495 registering with atransverse passage 496 in casing 472 which leads to the outer end ofextension 484 of the valve chamber 471, beyond the piston. Air from thevalve chamber can, therefore, by-pass around piston 482 via passages490, 491,- 494, valve chamber 493, and passages 495, 496. The upper andlower portions of valve chamber 493 are separated by a conical valveseat 497 on which seats a conical control valve 498. When this valve isclosed, the by-pass is shut off and the slide valve unit is under itsnormal effective pressure (Fig. 5). When, however, valve 498 is open,air by-passes from the valve chamber to the outer end of extension 484to move the slide valve unit reversely (Fig. 6), as above described. Toplace extension 484 under exhaust, while valve 498 is closed, at the topof valve chamber 493 is an inverse conical valve seat 499 beyond whichis a passage to atmosphere. On this valve seat seats an inverse conicalvalve 500. Both conical valves 498 and 500 are formed on a common valvestem 501 and are so arranged that when one valve is open the other isclosed. Valve 500 is a vent valve controlling communication between theinterior and exterior of valve casing 492. When valve 498 is open tobypass actuating air, valve 500 is closed to seal the valve chamber 493.When control valve 498 is closed to shut off the by-pass, valve 500 isopen, whereby air from the outer end of extension 484 exhausts via.passages- 496, 495 and valve chamber 493, as piston rod 481 moves underthe force of normal pressure.

To operate the by-pass control valve, as here shown as an example, theupper end of the valve stem 501 is connected by a coupling 502 with thecore 503 of a solenoid. This solenoid has a Winding 504 and a housing505 and is of any' suitable construction. Between the bottom of valve498 and a plug nut 506 is a return spring 507. The valve unit has aguiding tail-piece 508 sliding in nut 506. lVhen the solenoid isenergized the resulting core movement forces down the common valve stem501 and thereby closes vent valve 500 and opens by-pass valve 498. Thisposition is shown in Fig. 7 and corresponds a connected by pipes 328 and330 respectively.

to Fig. 6 in which the D-valve is moved to the right by the by-passingair. \Vhen the solenoid is de-energized, return spring 507 serves toreverse the common valve stem 501, thereby closing the by-pass valve4-98 and opening vent valve 500. This position is shown in Fig. 8 andcorresponds to Fig. 5 in which the D-valve is moved to the left by thenormal valve chamber pressure, the fluid previously by-passed exhaustingas described.

As shown, the piston movement to the right, as viewed in Figs. 5, 6, islimited by a stop lug 511 for engagement by the end of the piston rod.At the other end the closure plug 485 serves as a stop for the other endof the piston rod to limit movement to the left. This stop constructionavoids using the D- val've itself in stopping and so does notinterferewith the adapting movement of the D- valve.

The construction described, including the D-valve, its operatingpistons, its air-actuating system and the solenoid control valve,constitute one example of an air flow selective unit that may be termeda magnetic valve.

The above described features are those associated with the inlet valveof the hydraulic unit. A like control is associated with the exhaustvalve and it is unnecessary to show or describe the same in detail. Fig.2 shows a block 462a bolted to the common face of the cylinder casing452 that is a reverse hand duplicate of block 462 and bears the samerelation to the exhaust valve cylinder as block 462 does to the inletvalve cylinder. On the block 102a is a valve casing 472a that is areverse hand duplicate of valve casing 472. It will be understood thatthis casing contains a D-valve, operating pistons and associatedfeatures that are reverse hand duplicates of those described. Fig. 2also shows a solenoid unit duplicating that described, as will beapparent. That is, the two operating valve units have independentlyoperating controls so that the inlet valve and exhaust valve may beoperated independently. These magnetic valve units may be automaticallyoperated as described, for example, in the parent ap plication referredto.

In the embodiment illustrated in Fig. 1,

the'magnetic valves for hydraulic valve units 341, 34-l, are locatcd ata central station 335. The operating cylinders of unit 341 are connectedto this central station by pipes 3 12, 343, and those of unit 34-: bypipes 345, 3&6. Such an arrangement is more fully described in saidPatent No. LSstfLOll.

Also in this embodiment the operating cylinders of unit 323 areconnected by pipes 324 with a central station 325 having manuallyoperated valves for controlling the air flow. Valve units 327 and 329are similarly Cylinder 167 is also connected to station 325 by pipe 331.

Central station 325 has an air pressure supply line 326, a branch 336leading to station 335.

In some hydraulic systems it is desired to utilize relatively highpressure in certain steps and relatively low pressure in other steps.For example, in the apparatus above described, while the main ram andthe container pull-back are operated on high pressure, e. g. 5000pounds, it is desired to avoid this high pressure in the operation ofthe other hydraulic units such as the billet pusher and cutter and arelatively low pressure, e. g. 2000 pounds, is used. Means is provided,therefore, for limiting the main line pressure to a given low pressure,for example, by a low-pressure relief valve, and for electivelyrendering said relief valve ineffective so as to permit pressure tobuild up beyond such low limit. Constructions embodying the invention inits entirety will include means for also limiting the main line pressureto a given high pressure so that when the lowpressure relief isineffective the high-pressure relief will control. This may beaccomplished by two loaded relief valve units having different criticalloads, the low pressure unit having in addition, an elective dis chargevalve between its relief valve and the discharge water line. lVhen suchelective valve is open the low pressure unit functions but when suchvalve is closed the low pressure unit is cut out because even though itsrelief valve opens as normally, the water is checked by the electivevalve and consequently pressure can build up to the higher criticalpoint to be controlled by the high pressure unit.

Although capable of various constructions, in that here shown as anexample, and referring to Fig. 9, which shows the low pressure unit, aframe 716 carries a pressure cylinder 701 connected by an inlet 702 withthe main pressure line of a hydraulic system, e. g. by branch pipe 700of the main line of Fig. 1. In this cylinder is a plunger 703 working ina stuffing box 701-. Plunger 703, as will be apparent, is forcedupwardly by the main line pressure and a balancing load is provided toprevent such movement below a given critical pressure. While the loadingmeans may vary, it may conveniently be accomplish ed by fluid pressure.As here shown as an example, plunger 703 at its upper and outer endtakes into a socket formed in the bottom of a piston rod 705 on a piston706 working in a loading cylinder 707. Cylinder 707 is connected by apipe 708, through a valve chamber 709, with a tank 713 containingcompressed air. To avoid undue leakage, the air pressure may operatethrough a column of water which fills cylinder 707, being acted upon bythe air in the above mentioned receptacle. To this end, pipe 708 maylead almost to the bottom of the tank, the air driving the water upthrough the pipe .into the loading cylinder. Valve casing 709 contains askeleton valve 710 freely mounted in a conical valve seat 711 andlimited in its upward 'movement by a plug nut 712. The valve is arrangedto permit, when seated, a relatively slow flow of loading water intocylinder 707, but upon a reverse flow of loading water, out of cylinder707, valve 710 lifts from its seat and permits a relatively rapid flowthrough an unrestricted passage.

It will be seen that the load opposed to movement of pressure plunger703 is governed by the pressure of the loading air and the diameter ofpiston 706. By a proper combination of these two factors a balancingload for the desired critical pressure may be obtained. Assuming that inthe control unit being described the critical pressure is 2000 pounds,until that limit is reached the balancing load holds down piston rod 705 which in turn holds'down plunger 703 against the main line pressure.When, however, that limit is exceeded, plunger 7 03-is raised, forcingback 7 piston 705 against the load and this movement is utilized to opena relief valve. While the relieving means may vary, in structuresembodying the invention to what is now considered the best advantage,the relief valve will be positively controlled in its movements.Although capable of various constructions, in the embodimentillustrated, carried by frame 716 is a valve block 717 having ahorizontal bore 718 connected bya vertical bore 719 with a pipe 720which, in turn, is connected into the main pressure line. Between thevertical passage 719 and the end of horizontal bore 718 is a tubularelement 721 provided with a conical valve seat. Seating on this valveseat is a conical relief valve 722 formed on the end of a rotary valverod 723. This valve rod has a screwthrea'ded portion 724 (left handthread) working in an internally threaded stuffing box 725, and an endportion journalled in a bearing bracket 7 26. The valve is moved awayfrom and toward its seat by rotation of its valve rod and this iseffected, as shown,

. by movement of piston rod 7 05.

lVhile the connection between the latter piston and the valve rod mayvary, as here shown as an example, loosely mounted on the valve rod is apiston 7 which meshes with rack teeth 731 formed in the under side ofpiston rod 705. Keyed to valve rod 723 is a disk 732 having in'itsfacean annular channel (Fig. 11), blocked at a number of spaced intervals,e. g. four intervals, by abutment blocks 734. The channeled face of thisdisk abuts a plate 7 formed on the end of pinion 730. This plate hasfour lugs 736 which project into channel 733. Between each lug and oneof the abutment blocks 734 is a spring 737 housed by the channel.Assuming that the relief valve is open, when the pressure drops andpiston rod 705 moves down under its load, pinion 730 is rotated,counter-clockwise as viewed in Fig. 0, looking toward the left, each lug736 being pushed against its adjacent spring 737. This force istransmitted through the springs to blocks 734 to rotate disk 732 which,being keyed to the valve rod, rotates the latter. This rotation, throughthe left hand screwthread, moves the relief valve into its seat. Theteeth of pinion 730 are long enough to accommodate the endwise movementof the valve rod. The parts are so arranged that the valve is seatedshortly before the piston rod 7 05 completes its down stroke.Thereafter, the final rotary movement of the pin-- ion is taken up bythe compression of springs 737 through the movement of lugs 736. As aresult, the relief valve is not forced into its seat by the full load ofthe loading unit but is only under the force of compressed springs 737.

When critical pressure is exceeded and piston' rod 705 moves up, thepinion is reversely rotated, i. e. clockwise as viewed in Fig. 9. Theresulting movement of lugs 736 permits reexpansion of the springs 737,thus removing pressure from the seated valve. Continued movement of lugs736 brings them into engagement with the immediately adjacent blocks 734and thereafter disk 735 is reversely rotated by this engagement to totate the valve rod and withdraw the relief valve from its seat.

The relief valve described is always controlled in its movement by itsthreaded connection so that chattering, such as is usually encounteredin blow-0d valves, is avoided and the valve is capable of relativelylong life even under almost constant operation. The loading meansdescribed is such that there is relatively no inertia of mechanicalparts to be overcome in relief movement.

'Beyond the end of horizontal bore 718, valve block 717 has a verticallydisposed valve chamber 740 containing a tubular element 741 providing avalve seat. Cooperating with this valve seat is a conical valve 742carried on a valve stem 743 which extends down below the valve block.Valve 742 and its seat are located between the end of horizontal bore718. and discharge pipe 744 which may conveniently lead to the suctionside of the water pumps. In the presit ent' embodiment pipe 744 connectswith a pipe 745 (Fig. 1) leading to a storagetank 746 connected with thesuction side ofpumps 321. Valve 742 may be termed an elective valvebecause by its position election is made between an active 'or inactivelow pressure control. open, when relief valve 722 opens, water That is,if elective valve 742 is 15.0

from main line connection 720 is lay-passed throu h bores 719, 718,valve chamber 740, and ischarge connection 744, back to the suction sideof the pumps. But if elective valve 742 is closed, relief cannot takeplace even though relief valve 722 opens. Gonsequently, this lowpressure unit is cut out and pressure builds up to the higher limit. Theoperation of valve 742 will be referred to hereinafter.

Since pressure cylinder 701 is under main line pressure, packing 704exerts a considerable friction which tends to retard movement of thelunger 703. Ordinarily, therefore, the relief valve would not open atthe true critical pressure because its movement would be opposed by boththe balancing load and the friction referred to. There is provided meansfor counteracting this frictional drag on the valve-opening movement.Although capable of various constructions, as here shown as an example,sliding on-rods 750 adjacent piston rod 705 is a crosshead 751. Thiscross-head bears against two coil springs 752, the lower ends of whichbear against adjustably fixed abutments 753. Bearing against the top ofthe crosshead is a block 754 attached to piston rod 705. In the normalposition of the parts, that is, with the relief valve closed and pistonrod 705 down, springs 752 are compressed so that they tend, through thecrosshead and block,

to raise piston rod 7 05. The springs are so arranged that this tendencysubstantially counteracts frictional drag of packing 704. That is,relief movement of the parts is opposed by the load on piston 706 plusthe frictional drag of packing 704. Balanced against this is the mainline pressure plus the force of springs 752. Consequently, the valveopens at a point approximating true critical pressure.

When the critical pressure is exceeded and piston rod 705 movesupwardly, the springs.

expand. It will be apparent, therefore, that since they must bere-compressed upon the down movement of the piston rod, the parts cannotreturn to normal position upon a drop of pressure that is only slightlybelow critical pressure, because such reverse movement is op osed notonly by the main line pressure ut by the springs. As a result, therelief valve stays open until the main line pressure drops sufiicientlyto permit the balancing load to overcome the main line pressure andcompress the springs. The point of this drop will be considerablyremoved from the cr1tical pressure but it is noted that the system isnot designed to maintain a constant pressure but merely to preventexcess pressure. This substantial drop does no harm for once the reliefvalve is closed, the main line pressure quickly builds up again.

The high pressure unit, in the present embodiment, is basically aduplication of the low pressure unit except that it lacks a valvecorresponding to elective valve 742. Fig. 1 illustrates this highpressure unit. vThis view shows a tank 713a like tank 713 connected by apipe 708a to a loading cylinder 707a which corresponds to cylinder 707but is larger. As this unit is set for a higher critica-l(pressure, e.g. 5000 pounds, the balancing loa is correspondingly greater. This isconveniently accomplished by using the same loading air pressure andincreasing the diameter of the loading piston sufficiently to give thedesired balancin load value. Fig. 1 shows a valve block 717acorrespondin to block 717 but in which the horizontal ore 718a (Fig. 10)corresponding to bore 718, leads directly to a discharge connection 744acorresponding'to pipe 744 and connected to pipe 745. That is, there isno valve such as valve 742 between the relief valve and the dischargeline. It is to be understood that this high pressure unit has a reliefvalve and operating connections that are duplicates of like parts in thelow pressure unit. When elective valve 742 of the low pressure unit is'closedto cut out that unit, an, excess of main line pressure above thehigh limit causes the high pressure relief valve to open and pressure isrelieved by by-passing water via pipe 720a, bore 718a and pipe 744a tothe storage tank:

In the embodiment illustrated the highpressure unit has a supplementalfeature lacking in the low pressure unit. In hydraulic systems, such asthe extrusion press above described, there sometimes occurs a suddenbuildin u of pressure considerably beyond the.des1re critical pointSince the relief valve mechanism described requires some little intervalof time to function, there is provided a supplemental blow-oil valve forpreventing dangerous peak pressures. To this end, as here shown as anexam le bolted to valve block 117a of t e high pressure unit is asupplemental valve block 760. This block has a valve chamber in which islocated a bushing 763 having suitable openings for connection with abore 7 6-4 formed in the valve block and communicating with an inletpassage 7 66. Beyond the end of bushing 763 is a discharge passage 765.Seated in the bushing is a tubular valve seat element 762 having a crossbore 7 74 connecting, through the bushing openings, with the inlet. Theend of tubular element 762 is dished to form a conical valve seat for aconical blowofi valve'767. This valve is formed on the end of a valvestem 768 slidable in a packing 773 and spring-held to its seat by aloading spring 769. This spring is set; for a load at least as high asthe high critical pressure. The parts areso arranged that inlet 766connects with the water passage of valve block 717a inside the reliefvalve and discharge bore 765 connects with such passage outside (Fig. 12

1,'ssa,aea

the relief valve. That is, the water passage through supplemental valveblock 760 is a by pass around the relief valve of the high pressureunit. In case of sudden peak loads that might cause trouble before themain relief valve can open, valve 767 opens against its spring andallows passage of water around ;%he main reliet valve from pipe 7 20a topipe Ihe tubular element 7 62 has a stem 7 7 0 threaded in an adapter 763d and having a lock screw 771 on its outer end. In case the valve seatin the end of element 7 62 should wear, compensation can be effected bymanipulating stem 770 and lock screw 771 to move the seat element towardthe valve. Moreover, by manipulation of adapter 763a valve 767 can beground in position without being removed.

With the construction described, with the discharge passage between thevalve seat and the packing 773 for the valve stem, the packing is notunder main line pressure and consequently does not exert an unduefrictional drag on the movements of the valve stem.

The invention in its entirety includes means for automatically changingfrom one control to the other. This may be accomplished by normallymaintaining the system under low pressure control and, when highpressure is required, automatically causing the low pressure control tobe rendered ineffective. For example, in control systems such as thatabove described, the elective valve 742 may be kept open normally sothat the low pressure unit normally controls and, upon requirements forhigh pressure, causing closing of such valve to cut out the low pressurecontrol.

While the valve-pperating means may vary, it may conveniently beaccomplished by connecting valve stem 743 with the piston rod of anair-operated piston and controlling the air flow by a magnetic valvesuch as described. That is, valve 7 42 and its operating parts may beconsidered as the e uivalent of either hali of a hydraulic unit suc asthat described, e. g. the inlet valve half of the unit shown in Fig. 2.The operating parts are not shown in Fig. 9 but the construction will beapparent upon assuming valve stem 7 43 to correspond to valve stem 430of Fig. 2. Associated with the air cylinder, corresponding to cylinder438,

is a magnetic valve unit dupllcating that shown and described inconnection with the inlet valve of Figs. 2, 5 and 6.

While the control may vary, as here shown as an example, the solenoidcore 780 of the magnetic valve for the elective valve 7 42 is connectedin a loop 357, 781 in a D. C. line 353. In this line is a. normally openswitch S13 arranged to be closed when'the inlet valve of hydraulic unit323 opens. This may be accomplished by a suitable actuating arm (notshown) mounted on the protruding end of the inlet valve stem of unit323. Under what may be termed normal conditions, i. e. while the mainrain is. not under variable pressure and its inlet valve is closed,switch S13 is open, the solenoid of magnetic valve 7 80 is(ls-energized, its D-valve (in the position of Fig. 5) admits air to thebottom of the air cylinder for valve stem 743 and elective valve 742 isopen. Consequently, the low pressure control unit is active and the mainline pressure is limited to the low figure, c. g. 2000 pounds, for the,operation of such units as the billet pusher, slide and cutter. When,however, the main ram is to be ad vanced, thedemand for high pressure isput into edect by the opening of the inlet valve of hydraulic unit 323,and the opening movement of this valve closes switch S13. As a result,the solenoid of magnetic valve 780 is energized, its D-valve is reversed(to the position of Fig. 6), air is admitted to the top of the aircylinder for valve stem 7 43, and valve 742 is closed. Gonsequently, thelow pressure control is rendered inactive and the main line pressurebuilds up to the high figure, e. g. 5000 pounds. This condition existsas long as the inlet valve of hydraulic unit re mains open. When itcloses, switch S13 opens again and the parts return to originalposition.

In the present embodiment, high pressure is desired also in pulling backthe container to eject the sprue.- The container moves back, it will berecalled, under return pressure when the exhaust valve of its hydraulicunit 327 opens. The valve rod of this exhaust valve has aswitch-operating arm, like the arm for switch S13, and arranged to closea normally open switch S14 when such exhaust valve opens. This switchS14 is connected in a shunt 782 on loop 357, 781. Closing of this switchby the opening of the exhaust valve unit 327 results, as did closing ofswitch S13, in closing valve 742 and in rendering the lowpressurecontrol inactive. That is, when either of switches S13, S14 isclosed the sys tem is under high pressure control but when both are openit is under low pressure control. It will be apparent that various othercircuit arrangements for the control of valve 742 are possible. Thepressure may be controlled manually by a by-pass valve 321a between thepressure line andthe exhaust.

The operation of the apparatus will be clear from the above withoutfurther description.

What I claim is:

1. In a combination with the main pressure line of a fluid pressuresystem and means for building up pressure therein. a plurality of powerunits operated by said pressure, valve means for connecting anddisconnccting the respective power units with the line, a pluralityofcontrol units for limiting the fluid pressure to difi'erentpredetermined levels, selective means for selecting the particularcontrol unit to be effective, and means automatically operated in timedrelation with one of said valve means for operating said selectivemeans.

2. In combination with the main pressure line of a fluid pressure systemand means for building up pressure therein, a low-pressure control unithaving a relief valve capacitated to open upon a given main linepressure being exceeded, a high-pressure control unit having a reliefvalve capacitated to open upon a higher main line pressure beinexceeded, an elective valve for cutting 05 relief in the low-pressureunit even when said low-pressure relief valve is 0 en, whereby thelow-pressure control unit is rendered ineffective, a pluralit of powerunits for operation by said flui pressure, valve means for connectingand disconnecting the respective power units with the line, and meansautomatically operated by the operation of one of said valve meansforoperating said selective valve.

3. In combination with the main pressure line of a fluid pressure systemand means for building up pressure therein, a low-pressure control unithaving a relief valve capacitated to open upon a given main linepressure being'exceedeid, a high-pressure control unit having a reliefvalve capacitated to open upon a higher main line pressure beingexceeded, and an elective valve for cutting off relief in thelow-pressure unit even when said low-pressure relief valve is open,whereby the low pressure control unit isre'ndered ineffective.

4. In combination with the main line of a fluid pressure system andmeans for building up pressure therein, two power units connected insaid system for operation by the fluid pressure, controlling means 'forsaid power units, a low-pressure control-unit having a relief valvecapacitated to open upon a given main line pressure being exceeded, ahigh-pressure control unit having a relief valve capacitated to openupon a higher main line pressure being exceeded, and means forautomatically causing the low-pressure control unit to be renderedineffective upon operation of the controlling means for one of said.power units.

5. n combination with the main line of a fluid pressure system and meansfor building up pressure therein, two power units connected in said mainline, controlling means for said power units, a low-pressure controlunit having a relief passage connected in said main line, a reliefvalve-in said passage capacitated to open upon a given main linepressure being exceeded, supplemental elective valve in said reliefpassage, means including an electrically controlled element for holdingsaid supplemental valve open, and means operated a on the operation ofthe controlling means or one of said power units for" changing thecircuit condition of said electrically controlled element to cause thesupplemental valve to be closed, and a highpressure control unit havinga relief valve capacitated to open upon a higher pressure beingexceeded. 8

-6. In combination with the main line of a fluid pressuresystem andmeans for building up pressure therein, a pressure control unit having arelief assage connected to said main line, a normally closed reliefvalve in said passa a rotary valve rod for said relief valve, said valverod having a threaded portion in screw-threaded engagement with arelatively stationary part, and means dependent on a given main linepressure being exceeded for rotating said valve rod to open said valve.

7 In combination with the main line of a fluid pressure system and meansfor building up pressure therein, a pressure control unit having arelief passage connected in said main line, a normally closed reliefvalve in said passage, a cylinder open to main line pressure, areciprocating unit including a plunger in said cylinder, means foreffecting a counterbalancing load for said reciprocating unit, anoperating connection between said reciprocating unit and said reliefvalve, a packing for said plunger, and springmeans normally tending tomove the reciprocating unit in a direction to open the relief valve,thereby to counteract the frictional drag of said packing.

8. In combination with the main line of a fluid pressure system andmeans for building up pressure therein,-a pressure control unit having arelief passage connected in said main line, a normally closed reliefvalve in said passage, 8. cylinder open to main line pressure, areciprocating unit including a plunger in said cylinder and a piston rodand,

piston, means for exerting fluid pressure on said piston tocounterbalance the main line pressure up to a given value, and anoperating connection between said reciprocating unit. and said reliefvalve.

9. In combination with the main line of a fluid pressure system andmeans for building up pressure therein, a pressure control unit having arelief passage connected in said main line, a normally closed reliefvalve in said passage, a cylinder open to main line pressure, areciprocating unit including a plunger in said cylinder, means foreffecting a counterbalancing load on said reciprocating unit, and anoperating connection, including, a spring, between said reciprocatingunit and said valve.

'10. In combination with the main line of a fluid'pressure system andmeans for build ing up pressure therein, a pressure control unit havinga relief passage connected in said main line, a normally closed reliefvalve in said passage, a rotary screw-threaded controlled valve rod forsaid relief valve, means for causing rotation of said valve rod to opensaid valve upon a given main line pressure being exceeded, asupplemental valve block having a supplemental relief passage bypassingaround said relief valve, a normally closed supplemental relief valve insaid supplemental passage and spring-loading means for permittingopening of said supplemental relief valve at a predetermined main linepressure at least as high as said given pressure,

11. lln combinationwith the main line of a fluid pressure system andmeans for building up pressure therein, a valve block having a passageconnected in said main line, a tubular element having its interiorforming part of said passage, its inner end constituting a valve seat, aspring-loaded valve seating thereon, a threaded stem on said tubularmember in threaded engagement with a stationary part, and a head on thestem outside of the valve block by which the stem and its tubular membermay be manipulated.

12. In combination with the main pressure line of a fluid pressuresystem and means for building up pressure therein, a pressure cylinderconnected with said pressure line, a plunger operating therein, aloading piston, a piston rod thereon opposed to said plunger, a reliefvalve, an operating connection between said relief valve and said pistonrod, a loading cylinder for said piston, a tank for pressure fluid, aconnection between said. tank and said loading cylinder, and a throttlevalve in said connection arranged to permit relatively unrestricted flowout of said loading cylinder and relatively restricted flow into thesame, whereby the loading flow is throttled and the relief flow is free.

13. In combination with the main line of a fluid pressure system andmeans for building up pressure therein, two cylinders open to main linepressure, plungers in said cylinders, two relief passages for thepressure line, relief valves'in said passages, a connec tion betweeneach plunger and a relief valve for operating the valves, loading meansfor each of the operating connections comprising a piston and a commonsource of pressure fluid, said pistons being of different diameterwhereby the load valves are different, and supplemental means forclosing the relief passage of the low load unit to render said reliefpassage ineffective even with the relief valve 0 en.

14. In com ination with the pressure line of a fluid pressure system andmeans for building up pressure therein, a relief passage for saidpressure line, a valve for said passage, loading means including areciprocating element, means for causing the loading means to take apredetermined position, a connection including a yieldable elementbetween the loading means and the valve for closing the valve, and meansfor opening the valve upon agiven line pressure being exceeded.

15. In combination with the main pressure line of a fluid pressuresystem and means for building up pressure therein, a power unitconnected in said system for operation by fluid pressure, a pressurecontrol unit cooperating therewith and having a relief valve capacitatedto open upon a given main line pressure being exceeded, and an electivevalve for cutting ofi relief in said control unit even when said reliefvalve is open, whereby the control unit is rendered ineflective.

16. In combination with the main pressure line of a fluid pressuresystem and means for a building up pressure therein, two power unitsconnected in said system for operation by the fluid pressure atdifferent times and at different pressures, controlling means for saidpower units, a pressurecontrol unit having a relief valve capacitated toopen on a given main line pressure bein exceeded, and means forautomatically causing said control unit to be rendered ineffective uponoperation of the controlling means for one of said power units.

17 In combination with the main pressure line of a fluid pressure systemand means for building up pressure therein, two power units connected insaid system for operation by the fluid pressure, controlling means forsaid power units, a pressure control unit having a relief valvecapacitated to open on a given main line pressure being exceeded, anelective valve for cutting off relief in said control unit evenwhen'said relief valve is open, and means for automatically 0 cratingsaid elective valve upon operation of the controlling means for one ofsaid units.

18. In combination with the main line of a fluid pressure system andmeans for building up pressure therein, two power units connected insaid main line, controlling means for said power units, a low-pressurecontrol unit having a relief passage connected in said main line, arelief valve in said passage capacitated to open upon a given main linepressure being exceeded, a supplemental elective valve in said reliefpassage, means including an electrically controlled element for holdingsaid supplemental valve open, and means operated upon the operation ofthe controlling means for one of said power units for changing thecircuit condition of said electrical controlled element to cause thesupplemental valve to be closed, thereby to render said low-v pressurecontrol unit ineflective even when said relief valve is open.

19. In combination with the main pressure line of a fluid pressuresystem and means for building up pressure therein, two power unitsconnected in said system for operation b fluid pressure at diflerenttimes and at'di ferent pressures, fluid inlet and exhaust valves forsaid power units, a pressure control unit having a. relief valvecapacitated to open upon a given main line pressure bein" exceeded, anelective valve for cutting 0E relief in said control unit even when saidrelief valve is open, and means whereby said elective valve is closed tocut off such relief when the inlet valve of one of said units is open,and opened to permit such relief when said inlet valve is closed.

In testimony whereof, I have hereunto set m hand.

y DAVID L. SUMMEY.

